1. Field of the Invention
The present Invention relates to a double-clutch transmission which enables continuous shift transmission by a synchromesh mechanism with interruption of power transmission suppressed to a minimum by use of two clutches and two input shafts.
2. Description of the Related Art
As an automatic transmission of a vehicle, there is a double-clutch transmission. For the double-clutch transmission, for example, a constantly meshing gear mechanism in which a drive gear and a driven gear constantly engage with each other is used, which suppresses loss of power transmission during shift transmission.
For the structure of this double-clutch transmission, a structure that combines an input system using two clutches and two input shafts having drive gears with an output system using two output shafts having driven gears and a synchromesh mechanism is adopted.
Specifically, in the input system, for example, a plurality of advance shift levels are divided into shift level groups of an even number of shift levels and an odd number of shift levels. Each drive gear of the odd-number shift level group is installed to one of the first and second input shafts connected to a clutch, respectively. Each drive gear of the even-number shift level group is installed to the other input shaft. The rotational force of the engine is transmitted to the first and second input shafts via each clutch.
For the output system, there is used a structure to distribute each driven gear that meshes with each drive gear and a synchromesh mechanism that transmits the rotational force to each driven gear to the first and second output shafts installed in parallel to the first and second input shafts.
According to the above-mentioned input system and output system, for example, after the shift of the odd-number transmission shift level is finished, while the engine rotation to be input from the clutch to the first input shaft, that is, the motive force, is being generated from one output shaft, the drive gear of the subsequent even-number transmission shift level is synchronized with the other output shaft by the synchromesh mechanism to get ready for the gearshift operation of the subsequent shift level.
Consequently, when a gear is shifted in the subsequent shift level, the first input shaft is disconnected from the engine output shaft, and a clutch that connects the second input shaft to the engine output shaft is operated to connect them to change over to the shift level group that utilizes the second input shaft; then, immediately, the gear is shifted to the subsequent even-number shift level.
Then, when a gear is changed to the odd-number shift level, allowing the shift level of the first input shaft to get ready for the gearshift operation in the same manner as described above while the engine rotational force is being transmitted through the second input shaft can complete the gearshift operation to the subsequent odd-number shift level by changing over both clutches. Therefore, a loss of motive force transmission can be suppressed in the gearshift operation from a low-speed gearshift level to a high-speed gearshift level, for example, for first to sixth gear speeds.
This kind of technology is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2006-52832.
Note that, in this kind of double-clutch transmission, for control of the clutch operation, sensors to measure the rotational speed of the first and second input shafts are installed. Specifically, two sensors, one sensor that measures the rotational speed of the first input shaft and the other sensor that measures the rotational speed of the second input shaft, are installed.
On the engine side, a sensor that detects the engine rotational speed is installed. On the double-clutch transmission side, information on the engine rotational speed is conveyed. The double-clutch transmission controls the operation of each clutch in accordance with the engine rotational speed and rotational speeds of the first and second input shafts.
On the other hand, when the information on the engine rotational speed is not conveyed to the double-clutch transmission because, for example, the sensor that measures the rotational speed on the engine side fails, the automobile enters a failed state.
When the automobile enters such state, the shift position is fixed to, for example, the third gear speed to enable the automobile to travel to a safe place.
However, in the case where the shift position is changed to the third gear speed under the conditions that the engine rotational speed is not known, or in the case where the engine rotational speed does not correspond to the third gear speed, cases in which the clutch is destroyed, etc. may be assumed. Consequently, to control each clutch, for example, an auxiliary sensor that detects the engine rotational speed is installed on the engine side. This auxiliary sensor measures the engine rotational speed and the measurement results are conveyed to the double-clutch transmission side.
However, in a structure to install auxiliary sensors on the engine side to achieve fail-safe as described above, sensors increase in number.
When the number of sensors increases, consideration must be given to cost increase and installation space, which is not desirable.